CWEA Mechanical Technologist Grade 4
Advanced Exam Questions and Answers
Latest Update Pass Guaranteed
1. A centrifugal pump exhibits a 1X radial vibration amplitude of 0.45 in/s at 1780
RPM, but the amplitude drops to 0.08 in/s when the pump is operated at 1200 RPM.
The pump is direct-coupled to a 60 Hz motor. Which of the following is the most likely
root cause?
A. Misalignment of the pump and motor shafts
B. Resonance of the pump support structure near 1780 RPM
C. Hydraulic instability due to operation far left of the best efficiency point (BEP)
D. Inner race defect on the pump bearing
Answer: B. Resonance of the pump support structure near 1780 RPM
Rationale: The vibration amplitude is highly speed-dependent and peaks near the operating
speed, which is characteristic of a structural resonance. Misalignment (A) typically
produces high 2X axial vibration and is less speed-sensitive; hydraulic instability (C)
would vary with flow, not just speed; bearing defect (D) would show high-frequency
impacts, not a 1X peak.
2. During a routine oil analysis of a gearbox, the report shows a significant increase in
iron (Fe) concentration from 20 ppm to 150 ppm over 500 operating hours, with a
normal viscosity and no water contamination. The particle count (ISO 4406) is
18/16/13. Which maintenance action is most appropriate?
A. Immediately drain and replace the oil, then flush the gearbox.
B. Perform vibration analysis and thermography to correlate with wear debris.
C. Increase the oil change interval to 2000 hours to allow additive replenishment.
D. Add a desiccant breather to reduce moisture ingress.
Answer: B. Perform vibration analysis and thermography to correlate with wear
debris.
Rationale: Elevated iron with normal viscosity and no water suggests active wear, possibly
gear or bearing degradation. Vibration and thermography can localize the source before
invasive maintenance. Immediate oil change (A) may remove evidence but not fix the cause;
increasing interval (C) would accelerate damage; desiccant breather (D) addresses
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,moisture, which is not the issue.
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, 3. A mechanical seal on a raw sewage pump fails repeatedly after 2-3 months of
service. Inspection reveals a black, carbonized deposit on the seal faces and a
hardened elastomer. The pump is a dry-installed, back-pull-out centrifugal pump
operating at 1200 RPM. Which of the following is the most likely cause?
A. Excessive seal chamber pressure
B. Dry running or inadequate flush during startup
C. Incorrect seal face material for abrasive solids
D. Shaft misalignment exceeding 0.002 in
Answer: B. Dry running or inadequate flush during startup
Rationale: Carbonized deposit and hardened elastomer indicate overheating, often from
dry running or insufficient flush. Raw sewage pumps should have a flush plan (e.g., API
Plan 32) to cool and lubricate seals. High pressure (A) would cause extrusion, not
carbonization; abrasive solids (C) would show wear, not heat damage; misalignment (D)
would cause uneven face wear.
4. A plant uses a positive displacement rotary lobe blower for aeration. The blower is
rated for 1200 SCFM at 8 psig, but the discharge pressure has risen to 10 psig and the
motor current has increased by 15%. The inlet filter differential pressure is 2 in H2O
(normal). Which of the following is the most likely cause?
A. Increased system resistance due to fouled diffusers
B. Blower lobe wear causing increased slip
C. Incorrect timing of the lobes
D. Low inlet air temperature increasing air density
Answer: A. Increased system resistance due to fouled diffusers
Rationale: Higher discharge pressure and increased motor current indicate increased
system resistance, often from fouled diffusers or piping. Blower lobe wear (B) would reduce
pressure and flow; incorrect timing (C) would cause noise and vibration; low inlet
temperature (D) would increase density but not necessarily pressure to this extent.
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Advanced Exam Questions and Answers
Latest Update Pass Guaranteed
1. A centrifugal pump exhibits a 1X radial vibration amplitude of 0.45 in/s at 1780
RPM, but the amplitude drops to 0.08 in/s when the pump is operated at 1200 RPM.
The pump is direct-coupled to a 60 Hz motor. Which of the following is the most likely
root cause?
A. Misalignment of the pump and motor shafts
B. Resonance of the pump support structure near 1780 RPM
C. Hydraulic instability due to operation far left of the best efficiency point (BEP)
D. Inner race defect on the pump bearing
Answer: B. Resonance of the pump support structure near 1780 RPM
Rationale: The vibration amplitude is highly speed-dependent and peaks near the operating
speed, which is characteristic of a structural resonance. Misalignment (A) typically
produces high 2X axial vibration and is less speed-sensitive; hydraulic instability (C)
would vary with flow, not just speed; bearing defect (D) would show high-frequency
impacts, not a 1X peak.
2. During a routine oil analysis of a gearbox, the report shows a significant increase in
iron (Fe) concentration from 20 ppm to 150 ppm over 500 operating hours, with a
normal viscosity and no water contamination. The particle count (ISO 4406) is
18/16/13. Which maintenance action is most appropriate?
A. Immediately drain and replace the oil, then flush the gearbox.
B. Perform vibration analysis and thermography to correlate with wear debris.
C. Increase the oil change interval to 2000 hours to allow additive replenishment.
D. Add a desiccant breather to reduce moisture ingress.
Answer: B. Perform vibration analysis and thermography to correlate with wear
debris.
Rationale: Elevated iron with normal viscosity and no water suggests active wear, possibly
gear or bearing degradation. Vibration and thermography can localize the source before
invasive maintenance. Immediate oil change (A) may remove evidence but not fix the cause;
increasing interval (C) would accelerate damage; desiccant breather (D) addresses
Page 1 of 26
,moisture, which is not the issue.
Page 2 of 26
, 3. A mechanical seal on a raw sewage pump fails repeatedly after 2-3 months of
service. Inspection reveals a black, carbonized deposit on the seal faces and a
hardened elastomer. The pump is a dry-installed, back-pull-out centrifugal pump
operating at 1200 RPM. Which of the following is the most likely cause?
A. Excessive seal chamber pressure
B. Dry running or inadequate flush during startup
C. Incorrect seal face material for abrasive solids
D. Shaft misalignment exceeding 0.002 in
Answer: B. Dry running or inadequate flush during startup
Rationale: Carbonized deposit and hardened elastomer indicate overheating, often from
dry running or insufficient flush. Raw sewage pumps should have a flush plan (e.g., API
Plan 32) to cool and lubricate seals. High pressure (A) would cause extrusion, not
carbonization; abrasive solids (C) would show wear, not heat damage; misalignment (D)
would cause uneven face wear.
4. A plant uses a positive displacement rotary lobe blower for aeration. The blower is
rated for 1200 SCFM at 8 psig, but the discharge pressure has risen to 10 psig and the
motor current has increased by 15%. The inlet filter differential pressure is 2 in H2O
(normal). Which of the following is the most likely cause?
A. Increased system resistance due to fouled diffusers
B. Blower lobe wear causing increased slip
C. Incorrect timing of the lobes
D. Low inlet air temperature increasing air density
Answer: A. Increased system resistance due to fouled diffusers
Rationale: Higher discharge pressure and increased motor current indicate increased
system resistance, often from fouled diffusers or piping. Blower lobe wear (B) would reduce
pressure and flow; incorrect timing (C) would cause noise and vibration; low inlet
temperature (D) would increase density but not necessarily pressure to this extent.
Page 3 of 26
